Tracking blood flow into tissue (“perfusion”) is an important tool for medical diagnosis and research. Tissues require blood in order to survive and function; a decrease in perfusion (“ischemia”) is the principle mechanism in many of the major causes of mortality and morbidity, including myocardial ischemia, pulmonary embolism, and stroke. Perfusion also plays a critical role in cancer development. A tumor's capacity to augment blood flow by means of angiogenesis is a key limiting factor in cancer progression. Accordingly, diagnostic imaging techniques that can accurately and sensitively measure blood flow are needed for clinical and research studies.
Conventional methods for blood flow imaging have been proposed for a variety of imaging modalities including Positron Emission Tomography (PET), x-ray computed tomography (CT) and magnetic resonance imaging (MRI). PET methods include tracking radioisotope-labeled agents. These agents, added to the blood, emit positrons that are detectable by the PET scanning apparatus. In CT, iodated contrast agents are traditionally provided to the blood stream. The iodated contrast agents enhance the x-ray attenuation characteristics of the blood, increasing the contrast between the blood and surrounding tissue in the resulting CT image.